Variable resistance control utilizing metal foil to wire turns



NOV. 5, 1968 s. DE ET Al. 3,409,855

VARIABLE RESISTANCE CONTROL UTILIZING METAL FOI L TO WIRE TURNS FiledMarch 14, 1966 PLACING METAL FOIL ON STRIP 0F INSULATING MATERIAL.

l WINDING RESISTANCE HIRE AROUND STRIP AND FOIL.

OLINCHINO TERMINAL TO STRIP AND CUTTING STRIP TO LENOTN.

CUTTING FOIL ATENDS OF CENTER EOTION.

MOVING CUT OIL R WEEN RESISTANCE WIRE AND STRIP l LUXINO STRIP IN ACID,DIPPINS STRIP IN SOLDER.

FIGURE- 8 INVENTORS STANLEY O. BENDER F|GURE 4 I ROBERT E. EASH 251 256BYQQQW -5 Aru ula! United States Patent 3,409,855 VARIABLE RESISTANCECONTROL UTILIZING METAL FOIL TO WIRE TURNS Stanley 0. Bender, Berne, andRobert E. Eash, Decatur, Ind., assignors to CTS Corporation, Elkhart,Ind., a corporation of Indiana Filed Mar. 14, 1966, Ser. No. 533,878 6Claims. (Cl. 338-118) ABSTRACT OF THE DISCLOSURE Variable resistancecontrol having wirewound resistance element with shorted end turns. Apiece of metal is inserted at each end between several end turns of theresistance element and a winding strip to short adjacent turns at eachextremity of the resistance element. The pieces of metal are sweatedwith solder to the resistance element to insure a short circuitcondition between adjacent turns at each end of the resistance element.

The present invention relates to electrical controls, and, moreparticularly, to a variable resistance electrical control of the typecommonly referred to as a fader control and to a method of making thesame.

Variable resistance fader controls are commonly employed for changing inthe alternative the volume of the pair of loudspeakers. For example, inan automobile provided with front and rear loudspeakers, it ispreferable to adjust or balance the volume of both of the loudspeakerswith a single control thereby permitting the volume of one of theloudspeakers to be increased while the volume of the other loudspeakeris being decreased. The use of a single control also facilitatesadjustment of the volume of both loudspeakers to the same intensity atany given location.

Many types of fader controls are available on the market. In oneparticular type of fader control, the end turns of the resistanceelement are coated with a conductive paint to short-circuit the endturns of the resistance element. The conductive paints are, to a certaindegree, brittle and flexing or jarring of the resistance elementfrequently causes a crack in the conductive paint thereby increasing theresistance between adjacent end turns. In other fader controls, the endturns of the resistance element are covered with a metal strip. Suchconstruction, however, causes a step to be formed between the resistancepath and the edge of the strip resulting in an uneven feel or jump inthe shaft as the contactor is wiped across the step. Heretofore,attempts to short the end turns together with solder have beenunsuccessful since the resistance wire, e.g., Nichrome wire, formingthe'end turns generally contains chromium which is not Wettable bysolder. It would, therefore, be desirable to provide an improved fadercontrol construction employing a solder foil for shorting end turns andan improved method of shorting adjacent end turns of a resistanceelement therefor.

Accordingly, it is an object of the present invention to provide animproved fader control. Another object of the present invention is toprovide an improved method for shorting adjacent end turns of aresistance element employed in a fader control. An additional object ofthe present invention is to short adjacent turns of a resistance elementtogether by inserting an elongated strip of metal foil between the turnswound on a winding strip and then sweating the foil with solder to theturns. A further object of the present invention is to provide anelectrical control with a wirewound resistance element having some turnsat least partially embedded in a strip of metal foil. Further objectsand advantages of the present invention will become apparent as thefollowing description proceeds, and the features of noveltycharacterizing the in- M 3,409,855 1C Patented Nov. 5, 1968 vention willbe pointed out with particularity in the claims annexed to and forming apart of this specification.

Briefly, the present invention is concerned with an improved resistanceelement for a variable resistance fader control having a metal foilinserted between some of the turns of a resistance element and a windingstrip for shorting the turns together. In another embodiment the metalfoil is sweated with solder to the turns for shorting the turnstogether. The present invention is also concerned with an improvedmethod of shorting the end turns of a resistance element wherein anelongated strip of metal foil is initially placed against a windingstrip of insulating material. A resistance wire is then wound on thestrip of insulating material to secure the foil to the strip. Terminalsare clinched to the ends of the strip and electrically connected to thefoil and the resistance wire. The foil is then cut into three sectionsand the center section of the foil is removed from between theresistance wire and the insulating strip. If the strip is mounted in acylindrical housing, the strip is curled to the shape of the housing ofthe control before being assembled into the housing. For certainapplications, the electrical contact between the metal foil and theturns provides adequate shorting of adjacent turns. However, in apreferred form of the invention, the strip after being curled, is dippedinto a soldering flux to clean the foil and the resistance wire and thendipped in molten solder to sweat the foil to the adjacent turns. Afterthe sweating operation, the strip is washed and ready for assembly intothe housing of the fader control.

For a better understanding of the present invention, reference may behad to the accompanying drawings wherein the same reference numeralshave been applied to like parts and wherein: FIGURE 1 is an isometricview of an electrical control made in accord with the present invention;FIGURE 2 is an exploded view of the control shown in FIGURE 1; FIGURE 3is a side view of the resistance element of the control shown in FIGURE2 during various stages of manufacture; FIGURE 4 is a side view of theresistance element shown in FIGURE 3 after the terminals have beentrimmed; FIGURE 5 is a top plan view of the resistance element of FIGURE4 after the curling and sweating operation; FIGURE 6 is a cross sectionof the resistance element taken along line VIVI of FIGURE 5; FIGURE 7 isa grossly enlarged fragmentary section of the resistance element takenalong line VIIVII of FIGURE 4; and FIGURE 8 is a diagrammaticalrepresentation of the invention.

Referring now to the drawings, there is illustrated an electricalcontrol generally referred to as a variable resistance fader control andindicated at 10 comprising a cup-shaped metal housing 11 supporting aresistance element 20 and a rotor 30. Telescopically mounted within thehousing 11 and closing the open end of the cup-shaped housing 11 is aninverted cup-shaped insert 12 molded of a suitable insulating material.As shown in FIGURE 1, the end wall 12a of the insert 12 forms one of theouter end walls of the control 10 and the end wall 11a of the housing 11forms the other outer end wall thereof. The open end 11b of the housing11 is provided with a cutaway section and an arcuate boss 12b extendingradially outwardly from the insert 12 fits into the cut-away section 110of the housing 11 to orient the insert 12 with the housing 11. A skirt12c depending from the wall 12a and mounted within the housing 11insulates the resistance element 20 from the metal housing 11. Aplurality of tabs 13 integral with the housing 11 are folded over theend wall 12a of the insert 12 to secure the housing to the insert. Bothof the end walls 11a and 12a of the housing 11 and the insert 12respectively are'provided with apertures 14 and 15 and the rotor 30 isjournaled therein.

The resistance element 20 circumposes the rotor 30 and abuts against theinner wall of the depending skirt 12c 24b and the end turns of theresistance element are sweated to a pair of elongated strips of metalfoils 25a and 2512 (see FIGURES 4 and 5) shorting the end turns together(see FIGURE 7). The resistance element 20 is disposed in the insert 12with the upper edge of the resistance element 20 abuting against the endwall 12a for spacing the lower edge of the resistance element 20 awayfrom the end wall 11a of the housing 11. The end terminals 24a and 24bproject upwardly through slots 12d and 12e provided in the insert 12 andextend radially outwardly beyond the slots (see FIGURE 1) forming anangle supported on the walls defining the lower side of the'slots. Acollector ring 26 having an opening 26a abuts against the end wall 12aof the insert 12 and a center terminal 27 extends radially outwardlyfrom the collector ring 26 through a slot 12 provided in the insert 12.The rotor 30 molded of suitable insulating material is provided with acylindrical shoulder 30a engaging the inner edge of the opening 26a forpositioning the collector ring coaxially with the apertures 14 and 15.

For the purpose of transferring electric current from the resistanceelement 20 to the collector ring 26 a contactor 31 having a pair ofspaced contact fingers 32a and 32b electrically connected to each otherwipingly engages the resistance element 20. The contactor 31 comprises aring portion 31a in slideable engagement with the collector ring 26 anda pair of downwardly extending ears 33 integral with the contactor 31and received in a pair of diametrically disposed grooves 30b provided inthe rotor constrain the contactor 31 to rotate with the rotor 30. Inorder to limit rotation of the contactor 31, the rotor is provided withan arcuate boss 34 engageable with a stop 11d (see FIGURE 2) extendinginwardly from the end wall 11a of the housing 11. A hollow shaft 35fixedly secured to the rotor 30 extends outwardly of the housing and apair of tabs 35a extending axially from the shaft 35 may be flattenedoutwardly to secure a not-shown rotatable member thereto for rotatingthe contactor 31.

Referring now particularly to a preferred method of making theresistance element 20, the foil 25 (see FIG- URE 3) is unwound onto thewinding strip 21 of insulating material with a side of foil 25 flushwith the winding strip 21. The winding strip 21 and the foil 25 are thenfed into a winding machine and the resistance wire 22 is wound aroundthe winding strip 21 and the foil 25 securing the foil to the strip. Atpredetermined spaced intervals, pairs of terminals 23 (see FIGURE 3) areclinched to the winding strip electrically connecting the resistancewire and the foil to the terminals. The winding strip is then preferablycut to short lengths as shown in FIGURE 4 by removing a triangularsection 23a from each pair of terminals 23 to produce a resistanceelement 20 having a pair of end terminals 24a and 24b at the endsthereof.

The foil 25 between each pair of end terminals 24a and 24b is severedinto three sections, and the portion of the foil forming the centersection is removed from between the resistance wire 22 and the windingstrip 21 to space foil sections 25a and 25b. The resistance element 20with the foil sections on the outside of the strip is then curled (seeFIGURE 5) so as to fit inside of the insert 12, dipped in flux, andimmersed in molten solder to sweat the foil to the resistance wire andto the terminals. The resistance element is removed from the moltensolder and, after being Washed to remove the flux, the element is readyfor assembly into the insert 12. The resistance element can be dipped inmolten solder without shorting the 4 turns in the center section of theelement since the resistance Wire is not wetted by the solder. As bestshown in FIGURE 7, the contact resistance between the turns and the foilis decreased since the turns of the resistance wire, in addition tobeing in direct contact with the foil, also are partially embedded inthe metal deposits 28 bonded to the foil sections 25a and 25b. Theresistance element need not be curled if the control is of themetilineartype instead of the rotatable ty'pe. Moreover, it is to be understoodthat in certain applications the foil 25 need not be sweated to theresistance wire since the pressure contact formed between the foil andthe turns of the resistance wire by tightly winding the resistance wirearound the winding strip and the foil produces a sufficientl,y lowresistance connection. Only in preferred applications is the sweatingstep necessary. 1 I

In a particular embodiment, an elongated strip of'm'etal foil A.; inchwide and .001 inch thick was positioned'on awinding strip A inch wide.The foil can be ofnickel or any material, e.g., copper, easily wettableby a molten metal such as solder. A substantially thicker and moremalleable foil material is preferred when the sweating step iseliminated to reduce cost. It is critical, however, when the sweatingstep is employed that the foil does not melt in the molten metal. Thusthe foil material must have a substantially higher softening temperaturethan the molten metal and be readily wettable while the resistance wireshould be substantially unwettable. The resistance element 20 as bestshown in FIGURE 5 of the drawings is provided with a 240 shortingsection. By connecting the end terminals 24a and 24b of the resistanceelement of the fader control 10 to a pair of not-shown loudspeakers andthe center terminal 27 to one side of a not-shown input signal, rotationof the shaft 35 of the fader control 10 in one direction introducesresistance into the circuit of one of the loudspeakers decreasing thevolume thereof and removes resistance from the circuit of the otherloudspeaker increasing the volume thereof. The signal to both loudspeakers can also be balanced. The angle between the con'-= tact fingers32a and 32b generally is at least as large as the angle defined by theunshorted portion of the resistance element. Otherwise, all of theresistance could not be removed from both loudspeakers when the shaft isin the center position.

While there has been illustrated and described what is at presentconsidered to be a preferred embodiment of the present invention and amethod of making the same, and an additional embodiment thereof, it willbe appreciated that numerous changes and modifications are likely tooccur to those skilled in the art, and it is intended in the appendedclaims to cover all those changes and modifications which fall withinthe true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. A variable resistance control comprising a housing, a wirewoundresistance element disposed in said housing, said resistance elementcomprising a winding strip 'of insulating material, a resistance wirewound around the winding strip with adjacent turns spaced from eachother, a first piece of metal shorting a plurality of the turns of theresistance wire :at one end thereof to said first piece of metal to form.a first shorted end portion, a second piece of metal shorting aplurality of the turns of the resistance wire at the other end thereofto said second piece of metal to form a second shorted end portion, saidresistance wire having a single unshorted portion extending betweenthetwo shorted end portions, a first end terminal electrically connectedto said first shorted end portion of the resistance wire, a second endterminal electrically connected to said second shorted end portion ofthe resistance wire, and a contactor comprising a pair of spaced contactfingers wipin gly engaging the resistance element between the endsthereof, and a third terminal electrically connected with the contactor.

2. The control of claim 1, wherein a plurality of metal deposits arebonded to the first and second pieces of metal and at least partiallyembed the turns of the resistance wire shorted to the first and secondpieces of metal.

3. The control of claim 1, wherein said contact fingers are spaced aparta sufiicient distance to permit the simultaneous engagement of one ofsaid contact fingers with said first shorted end portion and the otherof said contact fingers with said second shorted end portion whereby theunshorted portion of the resistance wire may be effectively removed fromthe electrical circuits between the third terminal and the first andsecond-end terminals.

4. The control of claim 1, wherein the resistance element is curled withthe ends spaced from each other in the housing and the first and secondpieces of metal are disposed on the outer surface of the 'winding stripwith the contact fingers wipingly engaging the inside surface of theresistance element.

5. The control of claim 1, wherein the first and second end terminalsare integral with the first and second pieces of metal, respectively,and the distal ends of the first and second pieces of metal are securedto the resistance wire.

6. In a variable resistance control, the combination of a housinl awinding strip disposed in the housing, a resistance wire wound aroundthe winding strip, an elongated piece of metal disposed adjacent to andin electrical contact with a plurality of turns of the resistance wireon one side of the winding strip, means bonded to the piece of metal anddisposed between adjacent turns electrically connecting the adjacentturns to the piece of metal, and a movable contactor wipingly engagingthe resistance wire disposed on the other side of the winding strip.

References Cited UNITED STATES PATENTS 11/1955 Daniels 388-174 X

